The inventive concept relates to methods for manufacturing a solar cell and, more particularly, to methods for manufacturing a solar cell including a window layer.
Copper-indium-gallium-selenium (CIGS) thin film solar cells may be higher in efficiency than amorphous silicon solar cells. Additionally, an initial deterioration phenomenon may not occur in the CIGS thin film solar cells, such that these may have a relatively high stability. Thus, various techniques have been developed for commercialization of the CIGS thin film solar cells. The CIGS thin film solar cells may be replaced with single-crystal solar cells because of lightness and high efficiency thereof. The CIGS thin film solar cells may be capable of being used in space. The CIGS thin film solar cells may have the electricity generation amount per unit weight of about 100 W/kg. Thus, the CIGS thin film solar cells may have more excellent efficiency than silicon or GaAs solar cells having the electricity generation amount per unit weight of about 20 W/kg to about 40 W/kg. Currently, the CIGS thin film solar cells may have the efficiency of about 20.3% in a single junction structure. Thus, the CIGS thin film solar cells may have a capacity substantially equal to the maximum efficiency (e.g., about 20%) of an existing poly-crystalline silicon solar cells.
In spite of the above advantages, the CIGS thin film solar cells may have low productivity. Since CIGS thin film solar cells may be generally formed through various steps of vacuum processes, the CIGS thin film solar cells may have high manufacture cost and low mass productivity characteristics. The CIGS thin film solar cell may include a lower electrode, a light absorption layer, and a window layer that are sequentially stacked on a substrate. The window layer may include an intrinsic layer having high resistance and a transparent electrode having high electric conductivity. Generally, the window layer may be formed by a sputtering process using a plurality of targets corresponding to materials of the intrinsic layer and the transparent electrode respectively having electric characteristics different from each other. A sputtering apparatus may include a plurality of targets and a plurality of sputtering guns accelerating plasma ions to the plurality of targets when the window layer is formed. Thus, in a conventional art, a method of manufacturing a solar cell may require two or more targets and two or more sputtering guns during the formation of the window layer, such that a scale of the apparatus may become bigger and manufacture costs may become increased.